local.h

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#ifndef _ASM_X86_LOCAL_H
#define _ASM_X86_LOCAL_H

#include <linux/percpu.h>

#include <linux/atomic.h>
#include <asm/asm.h>

typedef struct {
    atomic_long_t a;
} local_t;

#define LOCAL_INIT(i)   { ATOMIC_LONG_INIT(i) }

#define local_read(l)   atomic_long_read(&(l)->a)
#define local_set(l, i) atomic_long_set(&(l)->a, (i))

static inline void local_inc(local_t *l)
{
    asm volatile(_ASM_INC "%0"
             : "+m" (l->a.counter));
}

static inline void local_dec(local_t *l)
{
    asm volatile(_ASM_DEC "%0"
             : "+m" (l->a.counter));
}

static inline void local_add(long i, local_t *l)
{
    asm volatile(_ASM_ADD "%1,%0"
             : "+m" (l->a.counter)
             : "ir" (i));
}

static inline void local_sub(long i, local_t *l)
{
    asm volatile(_ASM_SUB "%1,%0"
             : "+m" (l->a.counter)
             : "ir" (i));
}

static inline int local_sub_and_test(long i, local_t *l)
{
    unsigned char c;

    asm volatile(_ASM_SUB "%2,%0; sete %1"
             : "+m" (l->a.counter), "=qm" (c)
             : "ir" (i) : "memory");
    return c;
}

static inline int local_dec_and_test(local_t *l)
{
    unsigned char c;

    asm volatile(_ASM_DEC "%0; sete %1"
             : "+m" (l->a.counter), "=qm" (c)
             : : "memory");
    return c != 0;
}

static inline int local_inc_and_test(local_t *l)
{
    unsigned char c;

    asm volatile(_ASM_INC "%0; sete %1"
             : "+m" (l->a.counter), "=qm" (c)
             : : "memory");
    return c != 0;
}

static inline int local_add_negative(long i, local_t *l)
{
    unsigned char c;

    asm volatile(_ASM_ADD "%2,%0; sets %1"
             : "+m" (l->a.counter), "=qm" (c)
             : "ir" (i) : "memory");
    return c;
}

static inline long local_add_return(long i, local_t *l)
{
    long __i;
#ifdef CONFIG_M386
    unsigned long flags;
    if (unlikely(boot_cpu_data.x86 <= 3))
        goto no_xadd;
#endif
    /* Modern 486+ processor */
    __i = i;
    asm volatile(_ASM_XADD "%0, %1;"
             : "+r" (i), "+m" (l->a.counter)
             : : "memory");
    return i + __i;

#ifdef CONFIG_M386
no_xadd: /* Legacy 386 processor */
    local_irq_save(flags);
    __i = local_read(l);
    local_set(l, i + __i);
    local_irq_restore(flags);
    return i + __i;
#endif
}

static inline long local_sub_return(long i, local_t *l)
{
    return local_add_return(-i, l);
}

#define local_inc_return(l)  (local_add_return(1, l))
#define local_dec_return(l)  (local_sub_return(1, l))

#define local_cmpxchg(l, o, n) \
    (cmpxchg_local(&((l)->a.counter), (o), (n)))
/* Always has a lock prefix */
#define local_xchg(l, n) (xchg(&((l)->a.counter), (n)))

#define local_add_unless(l, a, u)               \
({                              \
    long c, old;                        \
    c = local_read((l));                    \
    for (;;) {                      \
        if (unlikely(c == (u)))             \
            break;                  \
        old = local_cmpxchg((l), c, c + (a));       \
        if (likely(old == c))               \
            break;                  \
        c = old;                    \
    }                           \
    c != (u);                       \
})
#define local_inc_not_zero(l) local_add_unless((l), 1, 0)

/* On x86_32, these are no better than the atomic variants.
 * On x86-64 these are better than the atomic variants on SMP kernels
 * because they dont use a lock prefix.
 */
#define __local_inc(l)      local_inc(l)
#define __local_dec(l)      local_dec(l)
#define __local_add(i, l)   local_add((i), (l))
#define __local_sub(i, l)   local_sub((i), (l))

#endif /* _ASM_X86_LOCAL_H */